1. Field of the Invention
This invention relates to sealing devices, particularly sealing devices for elongate electrical heaters.
2. Introduction to the Invention
Elongate electrical heaters are well known for use, for example, in the freeze protection and temperature maintenance of pipes. Particularly useful elongate heaters comprise (a) first and second elongate electrodes, (b) a plurality of resistive heating elements connected in parallel between said electrodes, e.g. a continuous strip of a conductive polymer in which the electrodes are embedded or which is wrapped around the electrodes, and (c) an insulating jacket which surrounds the electrodes and the heating elements. These heaters may be cut to the appropriate length for use in each application and the exposed ends must then covered. This is often accomplished by the use of wrapped tape, heat-shrinkable tubing or other sealing means. Such coverings may be bulky, craft-sensitive, and susceptible to moisture ingress.
End caps and sealing devices intended to provide electrical insulation and environmental protection to the cut ends are known. Some sealing devices serve not only to seal the ends and prevent the exposure to moisture, but also grip the heater in order to prevent pullout of the heater from the device during use. The device disclosed in U.S. Pat. No. 4,751,350 (Eaton), the disclosure of which is incorporated herein by reference, comprises a cap in which a plurality of resilient projections positioned at specific angles within the cap are used to grip an electrical cable. The cap provides a particularly effective seal when it is filled with a gel or other conformable material which effectively contacts the inserted cable.
When the heater comprises a conductive metal braid which surrounds the insulating jacket, the problem of making an effective seal becomes more difficult. The braid, which is for use in grounding the heater, accelerates the wicking of moisture down the length of the heater. In addition, the braid, which itself may be surrounded by an outer insulating jacket, interferes with the ability of a sealing device to adequately grip the heater. This may create a situation in which the braid can slip with respect to the insulating jacket, thus decreasing the "pullout force", i.e. the amount of force which is required to remove the heater from the sealing device. It is also necessary that the braid be removed or cut back from the end of the heater in order to prevent shorting of the electrodes to the braid.